Pressure sensitive device



Sept. 4, 1956 c. G. BEATTY ET AL 2,761,318

PRESSURE SENSITIVE DEVICE Filed Oct. 20, 1953 FIG. I

INVENTORS CHARLES G. BEATTY \YrlLLlAM O. OSBON ORNEYS United States Patent O PRESSURE SENSITIVE DEVICE Charles G. Beatty, Arcadia, Calif., and William O. Osbon, Pittsburgh, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary or the Navy Application October 20, 1953, Serial No. 387,336 3 Claims. (Cl. 73- 398) This invention relates to pressure sensitive devices and more particularly to apparatus which indicates deviations from selected fluid pressures. It is a portion of the apparatus described in the copending application Serial No. 385,983 filed October 13, 1953, of W. O. Osbon and Clinton R. Hanna, entitled Hovering System and assigned to the assignee of this invention.

It is an object of this invention to provide a new and improved apparatus for creating signals which are proportional to deviations from a selected fluid pressure.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein:

Fig. l is a sectional view of the device of this. invention; and

Fig. 2 is a circuit diagram showing the connections of the strain gages of Fig. 1.

Referring now to the drawing and more particularly to Fig. l, the reference numeral 21 designates an upper cylindrical container positioned on a lower cylindrical container 31 and communicating therewith through an opening 20. A cylindrical bellows 22 is secured to a lower wall of the upper container 21 to communicate with the opening 20, and a rigid circular plate 23 is secured to the upper wall of the bellows 22. A horizontal partition 33 is secured approximately midway in the lower container 31 and has a central opening 40. A plurality of evacuated cylindrical bellows 32 have their bottom ends secured to the partition 33 and carry a circular upper plate 34 on their upper ends. A cylindrical central bellows 35 is secured at its upper end to the upper plate 34 and is secured at its lower end to the partition 33 to surround the opening 40. The partition 33 and the central bellows 35 divide the lower container into an upper cavity 36 and a lower cavity 37. A rod 38 extends through the central bellows 35 and the opening 40 from the upper plate 34 to a lower plate 39. A plurality of springs 41 are positioned between the lower plate and the bottom wall of the lower container 31 to bias the upper and the lower plates 34 and 39 upwardly. The evacuated bellows 32 bias the upper and the lower plates 34 and 39 downwardly.

A housing 12 is divided by a flexible rubber diaphragm 13 into an upper chamber 18 and a lower chamber 17. The fluid, the variations of which are to be ascertained, is admitted into the lower chamber 17, and the upper chamber 18 connects, through a tube 14, with the upper container 21. A second tube 15, having a valve 16 therein, connects the tube 14 with the lower container 31.

A double-acting safety valve 19 is provided as a safeguard against excessive diflerences in pressure between the upper container 21 and the lower container 31. The safety valve 19 comprises a housing 48 in which are mounted two valve seats 46 and 47 which face in opposite directions and against which two valve disks 42 and 43 are biased by valve springs 44 and 45. The valves 19 are normally closed, but excessive pressure differences could be eliminated but will cause one of the valves to open to relieve the pressure. The purpose of the safety valves 19 is to limit the strain on the bellows 22 and on certain resistors which will be described subsequently.

The upper container 21, the upper cavity 36 and the tubes 14 and 15 are filled with a noncorrosive and electrically insulating fluid. The lower cavity 37 is filled with air. The diaphragm 13 may be omitted if the fluid, the pressure of which is to be ascertained, is such that it may safely be admitted to the containers 21 and 31.

Explanation The plurality of evacuated bellows 32 and the central bellows 35 in compartment 36 are used as a particular means for providing resiliency for the plate 34. The springs 41 in the air chamber 37 are used to supplement the physical limitations of the bellows under conditions when they are subjected to extreme pressure and might otherwise be damaged. conceivably, if the bellows were constructed of sufliciently stiff or strong material the springs 41 they are used to provide an efficient and practical device. The volumetric displace- 32 and 35 must be very ment of the group of bellows large in comparison with the volumetric displacement of the single bellows 22, in the upper compartment 21. This is in order to minimize the effect of pressure variations due to temperature changes which might occur in the liquid in the compartment 36. To this end additionally, the plurality of bellows 32 are evacuated to eliminate pressure variations which would otherwise occur by changes in the pressure of confined air within these bellows as the temperature in compartment 36 varies.

Operation In using the device, the valve 16 is opened and the fluid under pressure, the variations of which are to be determined is introduced into the lower portion 17 of the housing 12, causing the diaphragm 13 to flex. The flexing of the diaphragm 13 places the fluid in the tubes 14 and 15 and in the containers 21 and 31 under compression, and the bellows 32 and 35 and the springs 41 are compressed. After the bellows 32 and 35 have come to rest, the valve 16 is closed, sealing the fluid in the cavity 36 and maintaining it under the pressure which existed when the valve 16 was closed.

As long as the the bellows pressure of the fluid in the housing 12 increases, a pressure differential will be created across the bellows 22, and the bellows will be compressed until the pressures are again equalized. When the bellows 22 is compressed, the plates 23, 34, and 39 are moved downwardly. On the other hand, when the pressure of the fluid in the housing 12 is decreased, the bellows 22 and the plates 23, 34 and 39 spond by moving in the opposite direction. The displacement of the plate 23 from its intermediate position is proportional to the difference in the pressure of the fluid in the cavity 36, and the direction of its dispiacement denotes which of the two fluid pressures is the greater.

To produce an indication outside of the containers 21 and 31 of the position of the plate 23, tension sensitive resistors 24 and 25, often referred to as strain gage are secured to extend between the plate 23 and an upper wall of the container 21 and tension sensitive resistor 28 and 29 are secured to extend between the plate 23 and a lower wall of the container 21. The resistors 24, 25, 28 and 29 are prestressed by tensioning devices 26, 27, 51 and 32 respectively, and are connected by wires (not. shown) to a terminal housing 30 which is mounted on a.

side wall of the container 21. The resistors 24, 25, 28 and 29 are connected in the form of a Wheatstone bridge 61 as is shown in Fig. 2, with one end of the resistor 24 connected to one end of the resistor 29, the other end of the resistor 29 connected to one end of the resistor 25, the other end of the resistor 25 connected to one end of the resistor 28, and the other end of the resistor 28 connected to the other end of the resistor 24. Energy is supplied to the bridge 61 by a source of direct current 62 which is connected between the junction of the resistors 24 and 29 and the junction of the resistors 25 and 28, and the output of the bridge 61 is taken from a pair of terminals 68, one of which is connected to the junction of the resistors 28 and 24 and the other of which is connected to the junction of the resistors 29 and 25. The bridge 61 is balanced when the plate 23 is in its intermediate position, but when the plate 23 is displaced from its intermediate position, the changes in the stresses applied to the resistors 24, 25, 28, and 29 cause their resistances to change, unbalancing the bridge 61. When the bridge 61 is unbalanced, an output voltage is created across the terminals 68, the amplitude of which voltage is proportional to the amount of and polarity of which voltage is indicative of the direction of the displacement of the plate 23 from its intermediate position.

The described invention is sensitive to slight changes in pressure and has proven useful in automatic hovering apparatus for submarines. In addition, this invention has applicability as a telemetering sensing unit in steam, air or hydraulic systems to produce an indication Whenever the system pressure varies from the selected reference pressure. The output of this device may be indicated on a meter or may be used to actuate controls.

Obviously many. modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for determining pressure changes which comprises a housing, a transverse apertured partition in said housing dividing the housing into upper and lower liquid compartments, evacuated bellows means in said lower compartment having relatively large volumetric displacement and being deformable by pressure thereon, said bellows means being provided with bias elastically resisting such deformation, bellows means of relatively small volumetric displacement in the upper compartment closing off the aperture in the partition and adapted to be deformed responsive to difference between pressures in said liquid compartments, means for connecting the compartments to the same source of liquid under a given reference pressure to exert pressure on the several bellows means and and to deform the first said bellows means against the said bias, means to seal off the lower compartment to retain liquid therein at the reference pressure and means actuated by deformation of the bellows means in the upper compartment to indicate deviations from said reference pressure of pressure applied to said upper compartment after the lower compartment is sealed off.

2. Apparatus for determining pressure changes which comprises a housing, a transverse apertured partition in said housing dividing the housing into upper and lower liquid compartments, a group of evacuated bellows in said lower compartment providing relatively large volumetric displacement and being deformable by pressure thereon, said group of bellows being provided with bias elastically resisting such deformation, a single bellows of relatively small volumetric displacement in the upper compartment secured in the partition to close off the aperture therein and adapted to be deformed in response to difference between pressures in the compartments, means for connecting the upper and lower compartments to the same source of liquid under a given reference pressure for exerting pressure on the respective bellows in said compartments and deforming said group of bellows against the said bias, means to seal off the lower compartment to retain liquid therein at the reference pressure and means actuated by deformation of the single bellows in the upper compartment to indicate deviations from said reference pressure when additional pressure is applied to said upper compartment after the lower compartment is sealed off.

3. Apparatus as in claim 1, further characterized by strain gauge means in the upper compartment and being actuated by said single bellows to indicate deviation from the reference pressure.

References Cited in the file of this patent UNITED STATES PATENTS 2,452,799 Speaker et al. Nov. 2, 1948 2,509,621 Willoughby May 30, 1950 2,528,883 Hayward Nov. 7, 1950 FOREIGN PATENTS 15,937 Great Britain Nov. 11, 1915 134,731 Great Britain Nov. 13, 1919 396,819 Germany July 3, 1924 448,357 Germany Aug. 16, 1927 481,986 Germany Sept. 5, 1929 

